Rotary expansible drill bits



April 29, 1953 A. w. KAMMERER, JR 2,832,568

ROTARY EXPANSIBLE DRILL BITS 2 Sheets-Sheet 1 Filed May 26, 1955 INVENTORI W K444445252, rle.

AIea/Ee April 29, 1958 A. w. KAMMERER, JR 2,832,568

ROTARY EXPANSIBLE DRILL BITS INVENTOR. W KAMMEEEE, rle BY ATlZQ/VEYI 2 Sheets-Sheet 2 Filed May 26, 1955 Unite States Patent 6 ROTARY EXPANSIBLE DRILL BITS Archer W. Kammerer, Jr., Fullerton, Califi, assignor of three-fifths to Archer W. Kammerer and one-fifth to Jean K. Lamplzere, Fullerton, Calif.

Application May 26, 1955, Serial No. 511,188

18 Claims. (Cl. 255-76) The present invention relates to rotary drill bits of the expansible type capable of drilling or enlarging bore holes below strings of well casing through which the bits can pass to a greater diameter than the inside diameter of the particular casing string itself.

An object of the present invention is to provide an expansible rotary drill bit having cutters that feed the formation cuttings inwardly away from the formation shoulder on which the cutters are operating and also away from the wall of the enlarged well bore, to insure full removal of the cuttings from the region of drilling and unimpeded penetration of the cutters into the formation.

Another object of the invention is to provide an expansible rotary drill bit capable of enlarging the diameter of a well bore very eiiectively when subjected to heavy torque loads and drilling weights, thereby permitting hole enlargement to occur at a comparatively rapid rate.

A further object of the invention is to provide an expansible rotary drill bit having cutters capable of drilling effectively when subjected to heavy drilling weights, in which the penetration of the cutters into the formation is limited to prevent the cutters from being subjected to inordinately high torque loads.

Yet another object of the invention is to provide an expansible rotary drill bit capable of enlarging a well bore and of maintaining the enlarged hole concentric of the original well bore, the bit operating in a very smooth and stable manner. The smooth and stable operation is maintained despite drilling under heavy torque and drilling weight conditions.

Still a further object of the invention is to provide an eXpansible rotary drill bit in which the same size cutters can be used for enlarging the well bore to diiferent diameters.

Another object of the invention is to provide an expansible rotary drill bit, in which the bit is readily convertible, and in an economical manner, to the enlarging of well bores to various selected diameters.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of a form in which it may be embodied. This form is shown in the drawings accompanying and forming part of the present specification. It will now be described in detail, for the purpose of illustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

Referring to the drawings:

Figure l is a longitudinal section through an embodiment of the invention disposed in a well bore, the cutters and other parts occupying their initial retracted position;

Fig. 2 is a longitudinal section similar to Fig. 1, disclosing the cutters locked in their fully expanded position;

Fig. 3 is a cross-section taken along the line 33 on Fig. 2;

suitably secured to the body,

Fig. 4 is a. front elevational and partially sectional view of a portion of one of the cutter supporting members and cutter structures attached thereto;

Fig. 5 is a side elevational View taken along the line 5- 5 on Fig. 4;

Fig. 6 is a section taken along the line 6-6 on Fig. 4;

Fig. 7 is a section taken along the line 77 on Fig. 4;

8 is a section taken along the line 88 on Fig. 2.

As shown in the drawings, a rotary expansible drill bit A is secured to the lower end of a string of drill pipe B that extends to the top of the well bore C, and by means of. which the drill bit is lowered through a string of well casing (not shown) to a region therebelow where the hole enlarging operation is to commence. The general type of expansible drill bit disclosed in the drawings is illustrated and described in Patent No. 2,545,036, to which attention is invited for certain structural details.

The upper portion of the rotary drill bit consists of a mandrel 10 having an upper pin 11 threadedly connected to the lower end of the string of drill pipe B. This mandrel includes an upper kelly or drill stem member 12 slidably splined to the main body 13 of the drill bit. The exterior of the lower portion 14 of the kelly is noncircular in shape, being telescopically received in a companion non-circular socket 15 formed in the main bit body 13. Specifically, the kelly exterior and the socket '15 may be of hexagonal shape, to enable the kelly 12 to be moved longitudinally with respect to the body 13, while still being capable of transmitting rotary motion to the body.

The mandrel 10 has a limited range of longitudinal movement within the body, its downward movement being determined by engagement of the lower end 16 of the kelly with an inwardly directed body shoulder 17, and its upward movement being limited by engagement of an external shoulder or piston portion 18 of the kelly with a cylinder head 19 secured to the body. The upper end of the head has a flange 2i) engaging a body shoulder 21, the flange being prevented from moving upwardly of the body by snap retainer rings 22 fitting in a body groove 23 and overlying the flange 20. An annular guide 24 is releasably secured to the body 13 by a split snap ring 25 above the retainer rings.

The body 13 has a plurality of expansible parts mounted on it, These include cutter supporting members 2'6 pivotally mounted in body slots 27 on hinge pins 28 to prevent their loss therefrom. Each cutter supporting member 26 depends from the hinge pin 2;; and carries a drag cutter structure 29 at its lower end, which structure is specificallydescribed hereinbelow.

The cutter supporting members 26 and the cutter struo tures 29 themselves tend to occupy a retracted position substantially entirely within the confines of the main body 13 of the bit. These cutter supporting members and the cutter structures are expandible outwardly, to enlarge the sides of the well bo e C and to operate upon a formation shoulder E' that the cutter structures form in the latter. To accomplish the expansion, each cutter supporting member 26 has an inclined expander surface 30 on its inner portion below the hinge pin 28 which tapers in a downward and inward direction. Each expander surface terminates in a lock surface 31 formed on a lock portion of the cutter supporting member. The outward expansion is accomplished by producing relative longitudinal movement between the mandrel it and the bit body 13, which will produce relative longitudinal movement between the cutter supportingmembers 26 and the tubular member 33oF the mandrel It This tubular member includes a lower portion 34 slidable within a guide. bushing 35: mounted in a bridge 36 secured to the body and extending. acrossthebody slots .27.. This guide bushing is disposed below the lock portions 32 of the cutter supporting members 26.

Located initially substantially above the guide bushing 35 and below the hinge pins 28, and in cutter member recesses 37, is a mandrel lock and expander 38 which has outer surfaces 39 adapted to engage the expander surfaces 30 and the lock surfaces 31. The lock and expander 38 may be formed integral with the tubular member 33, the upper end of the latter being piloted within a socket 40 formed in the lower portion 14 of the kelly 12. An enlarged boss 41 on the tubular member 33 engages a downwardly facing shoulder 42 of the kelly, the tubular member being held against this shoulder by a suitable split retainer or look ring 43 snapped into an internal groove 44 encompassing the kelly socket and engaging the lower end of the tubular member boss 41.

Drilling mud or other fluid can pass down through the central passage 45 in the kelly or drill stern 12 and into the central passage 46 extending completely through the tubular member 33. Leakage of fluid around the exterior of the tubular member 33 is prevented by a suitable side seal ring 47, such as a rubber 0 ring, in a peripheral groove 48 in the kelly, which engages the interior of the boss 41.

Assuming that the body 13 of the tool is elevated relatively along the tubular mandrel 10, the inclined expander surfaces 30 of the cutter supporting members 26 will be shifted upwardly along the lock and expander portion 38 of the tubular member 33. During such upward shifting, the cutter supporting members 26, and the cutter structures 29 carried thereby, will be pivoted about the hinge pins 28 and urged in an outward direction. The upward movement of the body 13 withrespect to the tubular mandrel 10 can continue'until the cutter structures 29 have been shifted outwardly to their fullest extent, as determined by engagement of stop shoulders 49 on the cutter supporting members 26 with companion shoulders 50 formed in the body on opposite sides of the body slots 27. When such engagement occurs, the lower end 16 of the kelly portion 12 of the tubular mandrel will engage the body shoulder 17, and the lock and expander 38 on the tubular member 33 will be disposed behind and in engagement with the lock portions 32 on the cutter supporting members 26.

It is to be noted that the surfaces 31 of the lock portions 32 of the cutter supporting members 26 and the companion surfaces 39 on the lock and expander portion 38 of the tubular member are substantially parallel to the axis of the drill bit, to prevent the reactive forces of the formation on the cutter structures 29 from moving the latter inwardly. As a practical matter, it is pre ferred that the coengaging lock surfaces 31, 39 be inclined slightly in a downward direction toward the axis of the tool, to insure release of the lock and the expander portion 38 from the cutter supporting members 26 when the latter and the cutter structures 29 are to be shifted to retracted position.

The relative longitudinal movement between the tubular mandrel 10 and the body 13 of the tool is accomplished hydraulically in the specific form of apparatus disclosed in the drawings. Thus, the piston or enlarged portion 18 on the drill stem 12 is received within a counterbore 51 formed on the upper portion of the body of the tool. This upper portion actually constitutes a cylinder 52 having a cylindrical wall 53 extending from a lower shoulder 54, defining the bottom of the counterbore 51, to the cylinder head 19.

A confined cylinder space 55 is formed between the piston portion 18 of the kelly, the periphery of the kelly above the piston, and the cylinder 52. A suitable packing or side seal ring 56 may be disposed in a suitable piston ring groove 57 formed in the piston 18, which is adapted to slidably seal against the cylindrical wall 53 of the cylinder 52. Fluid is thereby prevented from passing in a downward direction between the piston and 4 the cylinder. Similarly, fluid is prevented from passing in an upward direction out of the annular cylinder space 55 by an inner side seal ring 58 carried in an internal groove 59 in the cylinder head 19 and slidably and sealingly engaging the periphery of the kelly 12 above the piston 18, and also by an outer side seal ring 60 disposed in an external groove 61 in the head 19 and sealingly engaging the cylinder wall 53. 1

Fluid under pressure in the string of drill pipe B and i=1 the in liar mandrel passage 45 can be fed into the cylinder space 55 through one or more side ports 62.

establishing communication between the central passage 45 through the kelly and the cylinder space. Such fluid under pressure is developed, in the form of invention 4% d in the drawings, by virtueiof the fact that the p sage 46 through the tubular member 33 of the mandrel 1'1 is of a restricted diameter as compared to the passage 45 through the kelly portion of the mandrel. As a result, the pumping of drilling mud, or other fluid, at an adequate rate through the apparatus will build up a back pressure of fluid in the passage 45, which pressure will be imposed on the fluid in the cylinder space 55, acting upon the cylinder head 19 to urge the body 13 of the tool in an upward direction with respect to the tubular mandrel 10, to secure the outward expansion of the cutter supporting member 26 and cutter structures 29 to their fullest extent, as above described.

As disclosed, three sets of supporting members 26 and supporting structures 29 are employed, displaced substantially 120 degrees apart from each other, to secure a smoothly running rotary expansible drill bit. Each cutter structure 29 is removably secured to the lower portion of a cutter supporting member 26. As specifically disclosed, the lower portion of the cutter supporting member 26 is provided with a lateral groove 63 extending upwardly from its lower end, and terminating in an inner or back wall 64. The groove 63 is defined by parallel, longitudinally extending side walls 65 terminating in a concave upper end wall 66. The inner portion 67 of the cutter supporting member extends downwardly below the lower end of the groove 63, to form a lower abutment for the cutter structure 29 itself, as described hereinbelow. 7

Each cutter structure 29 includes a transverse base 68 engaging the lower end 69 of the supporting member on opposite sides of the longitudinal groove 63. The inner face 70 of this base engages the depending portion 67 of the back wall 64 extending below the groove 63. Integral with and extending upwardly from the base is a central rib 71 which makes a relatively snug fit in the groove 63. This rib has opposed side walls 72 companion to the side walls 65 of the groove, and an upper convex end 73 having substantially the same curvature as the concave upper groove wall 66. The rib 71 extends inwardly from the outer surface of the supporting arm 26 to the back wall 64 of the groove. In efiect, the outer surface 74 of the rib may form a continuation of the outer surface of the cutter supporting arm 26.

The cutter structure 29 is removably secured to the cutter supporting arm or member 26 by a bolt 75, which passes through aligned holes 76 in the supporting member 26 on opposite sides of the groove 63, and also through a transverse hole 77 in the central rib which is slightly eccentric of the supporting member holes 76. The hole 77 through the rib is preferably greater in diameter than the holes 76 through the supporting member 26, with its center or axis disposed slightly downward and outward of the common axis of the supporting member holes 76. The bolt 75 passes through the supporting member holes 76 and the ec'centrically disposed or offset hole 77 through the cutter structure rib. The shank 78 of this belt may .make a sliding fit with the supporting member holes 76 and is forced through the hole 77 in the central rib 71in such manner that it urges the cutter structure 29 in an inward and upward direction with respect to the supporting member 26. This is due to the eccentric disposition of the hole 77 in the supporting rib. Thus, the bolt 75 will move the cutter structure 29 inwart'iy, to engage the inner face of the rib '71 with the back wall 64 of the groove, and also to snugly engage the inner face of the cutter base 68 with the depending portion 67 of the cutter supporting member 26 below the groove 63. At the same time, the cutter structure 29 is urged in an upward direction, to place the upper surface of the cutter base 68 snugly in engagement with the lower surfaces 69 of the supporting member 26 on opposite sides of the groove 63, and also to place the convex upper end 73 of the rib snugly in engagement with the concave upper wall 66 of the groove 63. It is evident that the bolt 75, when forced through the several holes 76, 77, will, in effect, shift the cutter structure 29 diagonally in an upward and inward direction, to form a snug engagement between the several surfaces referred to on the cutter structure 29 and the opposed surfaces on the cutter supporting member 26.

The head 79 of the bolt may be received partially or completely within a counterbore 80 formed in one side wall of a cutter supporting member 26, a nut 61 being threaded on the other end of the bolt shank '73 and bearing against the other side wall of the cutter supporting structure 26, as a result of appropriately tightening the r nut on the bolt shank. After the nut 81 has been tightened, the threaded end of the shank 78 may be peened over against the nut 81 to lock the latter in place.

Each cutter structure 29 is provided with a plurality, such as a pair, of teeth 82, 83 that are integral with and depend from the base 63 of the cutter structure 29. As specifically disclosed, a forward tooth or blade 82 is located at the forward portion of the cutter base 68 and extends from the outer end of the base substantially to its inner end. This blade 82 is shaped to operate upon the formation shoulder B when expanded outwardly to its maximum position, its lower edge 82a engaging the shoulder E. It is provided with a longitudinal reaming surface 84, or edge, that is adapted to engage the wall of the enlarged hole F, in order to ream the latter to its proper diameter. The blade 82 is of sufficient length laterally of the well bore as to extend at least from the wall of the original hole C to the wall of the enlarged hole F.

A trailing blade also depends from the base 68 of the cutter structure 29. This trailing blade is also adapted to operate upon the formation shoulder E after the cutter supporting member 26 and cutter structure 29 have been expanded outwardly to their maximum position. It has a longitudinal reaming edge 85 adapted to operate upon the wall of the enlarged well bore F, the lower blade edge 86 operating upon the transverse formation shoulder itself.

Both the forward and rearward blades 82, 83 are nonradial of the axis of rotation of the expansible rotary drill bit. It is preferred that they be provided with a negative rake, each of them lying in a plane passing to one side of the axis of the apparatus. The stability in the operation of the apparatus is increased if the blades 82, 83 have different rakes. Thus, the forward blade 82 has a substantially greater degree of negative rake than the trailing blade 83. The two blades 82, 83 may be at an acute angle with respect to each other.

Because of the negative rakes of the blades 82, 83 they will operate upon the formation shoulder E to produce cuttings, shifting the latter inwardly away from the wall of the enlarged hole F toward the center of the latter, thereby facilitating the displacement of the cuttings from the ormation wall and the shoulder E to a region where they can be effectively removed by the drilling fluid. Accordingly, the negative rake of the blades insures that they will remove the cuttings from the drilling region and also insures the maximum penetration of the blades into the formation.

Since the forward and trailing blades or teeth 82, 83

' are disposed at an acute angle to each other, the trailing blade 83 does not extend inwardly to as great an extent as 6 the forward blade, providing a space therebetween through which the cuttings produced by the trailing blade 83 can readily pass in an inward direction.

As specifically disclosed, the lower edges 82a, 86 of the forward and trailing blades 82, 83 are substantially normal to the axis of the apparatus when the cutter structures 29 and supporting members 26 have been expanded outwardly to their fullest extent. At this time, the outer reaming edges 84, S5 of these blades are substantially parallel to the axis of the apparatus. The rib "i1 is also provided with a reamer blade 38, which is in an inclined position when the cutter structures 29 have been expanded outwardly to their maximum extent, the inclination being in an upward and inward direction. However, when the cutter structures 29 and cutter supporting; members 26 are disposed in their inward retracted position, the reamer portions 88 of the ribs will be disposed substantially lengthwise of the wall of the well bore C which is to be enlarged. At this time, the lower cutter blades 82, 83 themselves occupy an inclined position, with their reamer surfaces 84, $5 inclined in an inward and downward direction, as clearly shown in Fig. 1. As the expansion of the cutters 29 proceeds, the reamer edges 88 of the ribs will engage the wall of the formation and will facilitate the initial production of anenlarged well bore, and the outward expansion of the cutter structures 29 and cutter support ing members 26 to the maximum extent disclosed in Fig. 2.

When the cutter supporting members 26 have been expanded outwardly to their maximum extent, their op posed shoulders 49 engage companion shoulders 50 on the main body 13 of the drill bit. The tapered shoulders 49 on each cutter supporting member 26 and the companion shoulders 50 on the body are: inclined in a downward and outward direction, so that the coengagement of the supporting member shoulders with the body shoulders causes a wedge-like action to occur between the two parts, tending to prevent transverse motion of the cutter supporting members'26 during the operation of the drilling tool, the coengaging tapered or inclined shoulders tending to maintain each cutter supporting member appropriately located in its slot 27. In the absence of the inclined shoulders, relative transverse shifting of the cutter supporting members 26 with respect to the body 13 to a slight extent could occur, which can shorten the life of the parts.

The lower portion of the apparatus disclosed includes a pilot structure 89 that does not form part of the invention claimed in this case, which has the purpose of centering the apparatus in a previously drilled hole C. This pilot structure is mounted on the lower portion of the body 13 below the body slots 27. Such body portion below the body slots is provided with an enlarged cavity 9i! opening upwardly into the slotted portion of the body, this cavity terminating in a lower wall 91 that has a relatively small diameter hole 92 for fluid passage therethrough and for discharge into the well bore below the apparatus. The diameter of the passage 92 in the lower portion of the body is relatively small, to retard the flow of fluid in a downward direction from the enlarged cavity 90, the fluid in the latter remaining as relatively dead fluid against which fluid from the mandrel It will discharge, the fluid then being deflected laterally from the dead fluid toward the cutter structures 29,. to clean them and maintain them clean of cuttings, as well as to carry the cuttings in an upward direction around the apparatus and the drill pipe B to the top of the hole.

To facilitate the spraying action of the fluid being discharged from the mandrel 10, the lower portion of the tubular member may have a nozzle or bean 93 suitably secured therein which will jet the fluid onto the relatively dead fluid in the cavity 90, whereupon such fluid will spray laterally outward through the body slots 27 and onto the cutters 29. By providing the dead fluid, the fluid stream cannot strike directly against the me- 9 7 tallic parts of the body, to cause erosive wear thereon. The relatively dead fluid acts as a cushion for the side wall 90a and bottom 91 of the enlarged cavity, enhancing the life of the parts considerably.

in the operation of the apparatus A, it is run in the well casing with the cutter supporting members 26 and the cutter structures 29 in their initial retracted position, such as shown in Fig. l. The wall of the well casing prevents the outward expansion of the cutters, the reamer blades 84, 85, 39 of the cutter structures 29 merely sliding along the wall of the casing during descent of the apparatus. When the apparatus has been lowered below the lower end of the casing, and is located in open 'hole C, the pumps at the top of the well bore are started, to pump fluid at a suflicient rate through the drill pipe and into the mandrel passages 4-5, 46, building up a back pressure in the kelly passage 45 and in the fluid in the ports 62 and cylinder space 55, which pressure will act upon the cylinder head 19 to urge the body 13, the cutter supporting members 26 and the cutter structures 29 in an upward direction with respect to the mandrel 10.

During such upward movement, the expander surfaces 30 of the cutter supporting members 29 are brought to bear against the lock and expander portion 38 of the mandrel, the cutter structures 29 being urged in an outward direction against the wall of the well bore. The drill pipe B and the rotary drill bit A are rotated at the proper speed while fluid is being pumped through the apparatus, the reamer edges 88 on the ribs '71 first enlarging the well bore, which enlargement is assisted when the cutter supporting members 26 and cutter structures 29 have been shifted outwardly to the point at which the reamer edges 84, 85 of the depending blades 82, 33 engage the wall of the well bore. As the various reamer portions of the cutters enlarge the well bore, the hydraulic force acting upon the body 13 raises it and the cutter supporting members 26 and cutter structures 29 to a further extent, until the cutters are fully expanded outwardly to the maximum extent, as determined by engagement of the inclined supporting member stop shoulders 49 with the companion inclined body stop shoulders 54) and the lower end 16 of the kelly portion of the mandrel with the body shoulder 17. With the parts in this position, the lock portions 32 of the cutter supporting members 26 will bear against the lock and expander portion 38 of the tubular member 33, to preclude inadvertent partial retraction of the cutter structures 29 from their fully expanded position.

Downweight of the proper amount is now imposed on the string of drill pipe B, this downweight being transmitted through the kelly 12 to the body shoulder 17, and from the body through the stop shoulders 50, 49 directly to the supporting members 26 and the cutter structures 29, urging the blades 82, 83 of the latter into the transverse formation shoulder E previously produced to drill away the formation shoulder and enlarge the well bore to the required diameter and along the desired length of hole. During the drilling action, the blades 82, 83 will feed the cuttings inwardly away from the wall of the enlarged hole)? and toward the body of the tool where the fluid being discharged from the lower end of the mandrel will strike the dead fluid in the cavity 90 and be sprayed in an outward direction through the slots 27, carrying the cuttings upwardly to the top of the well bore. In addition, the reamer edges 84, 85 will engage the wall of the enlarged well bore F, to insure that it is being drilled to the proper gauge.

in view of the negative rake or angle that the cutter blades 82, 83 make with respect to the axis of the tool, not only are the cuttings fed inwardly away from the formation, but the blades shear the formation material off the shoulder E rather than merely scraping it off. In the absence of the negative rake, the blade action would be such that it would tend to trowel or plaster the retracted position, such as disclosed in Fig. l.

cuttings against the wall of the hole P, which would irnpede drilling progress.

It is to be noted that with the three sets of equiangularly displaced cutter supporting members 26 and cutter structures 29, and the provision of two cutter blades 82, 33 on each cutter structure, there are six lines or regions of contact of the apparatus against the transverse'formation shoulder E and also against the wall of the hole F. Such extensive regions of contact insure the drilling of a concentric hole and the smooth operation of the apparatus. Such concentric hole production and smooth operation occurs despite the imposition of relatively heavy drilling weights on the cutters 82, 83, which will normally be attended with correspondingly heavy torque loads being imposed thereon. The large surfaces in contact permit relatively heavy drilling weights to be imposed on the tool without the danger of breaking off of the shoulder E, which might provide irregularity in the operation of the apparatus.

Despite the fact that the tool can be operated with heavy drilling weights imposed on its cutters, the penetration or" the blades 32, 83 of the latter is limited by the base 65; of each cutter structure 29. The blades will not penetrate to a greater extent than is permitted by the contact of the base 68 of each cutter structure with the formation shoulder E itself.

in the event it is desired to retrieve the apparatus from the well bore after the hole enlarging operation has been completed or as a result of the cutter structures becoming worn, it is only necessary to discontinue the pumping of the drilling fluid through the drill pipe in the apparatus, to relieve the pressure in the cylinder 52, and to elevate the drill pipe B. Such elevating movement will elevate tne tubular mandrel 10 with respect to the body 13 and the cutter supporting members 26, to raise the lock and expander portion 38 above the expander surfaces 30, whereupon the cutter structures 29 can drop back to their In the event the cutters are reluctant to move to such position, the outer surfaces of the cutter supporting members 26 will engage the casing shoe upon elevation of the apparatus in the well bore, which will force them inwardly, enabling the apparatus to be drawn into the well casing and elevated to the top of the well bore.

At the top of the well bore, the worn cutters '29 can be replaced merely by removing the bolts 7:3, new or rebuilt cutter structures then being mounted on the cutter supporting members 26 in their place. Because of the ease or assembly and disassembly of the cutter structures 29 with respect to the supporting members 26, the same cutter structures 29 can be used for drilling a plurality of: sizes of holes. The cutter supporting arms 26 selected will be such as to coact with the expander 38 and produce the outward expansion of the cutter structures 29 mounted thereon to the proper extent. The groove 63 and lower portion of each cutter supporting member 26 need merely be placed therein in such position that each cutter structure 29, when mounted thereon, will occupy the proper position in the well bore upon being expanded outwardly to the maximum extent. That is to say, the groove 63 and lower portion of each cutter member 26 is so shaped that the rcarner edges 84, 85 ot' the blades are disposed substantially parallel to the axis of the apparatus when the cutters have been expanded outwardly to their maximum extent.

It is, accordingly, apparent that it is unnecessary to provide complete combinations of supporting members 26 and cutter structures 29 to drill diiferent size well bores. The same cutter structure 29 can be used, such cutter structure merely being mounted on dimensionally different cutter supporting members 26.

The inventor claims:

1. In a rotary drill bit to be lowered in a well bore: a main body; cutter means mounted on said body for expansion laterally outward of said body; means for expanding said cutter means laterally outward of said body for operation upon a transverse formation shoulder in the well bore; said cutter means including leading and trailing cutter blades adjacent to one another having different negative rakes and engageable with the formation shoulder, said blades having longitudinally extending reamer edges engageable with the wall of the well bore when the cutter means has been expanded outwardly of said body.

2. In a rotary drill bit to be lowered in a well bore: a main body; a cutter supporting member mounted on said body for expansion laterally outward of said body; leading and trailing cutter blades secured to said member adjacent to one another; means for expanding said supporting member and cutter blades laterally outward of said body; said cutter blades having bottom cutter edges and side cutter edges engageable with the wall of the well bore; said cutter blades having different negative rakes.

3. in a rotary drill bit to be lowered in a well bore: a main body; a cutter supporting member mounted on said body for expansion laterally outward of said body; leading and trailing cutter blades secured to said member adjacent to one another; means for expanding said supporting member and cutter blades laterally outward of said body; said cutter blades having bottom cutter edges t and side cutter edges engageable with the wall of the well bore; said cutter blades having different negative rakes: the negative rake of said leading blade being substantially greater than the negative rake of said trailing blade.

4. In a rotary drill bit to be lowered in a well bore: a main body; a cutter supporting member mounted on said body for expansion laterally outward of said body; leading and trailing cutter blades secured to said member; means for expanding said supporting member and cutter blade laterally outward of said body; said cutter blades having bottom cutter edges and side cutter edges; said cutter blades having different negative rakes; the side cutter edges of said blades being substantially equidistant from the axis of rotation of said main body; one of said blades extending laterally inward from its side cutter e edge a substantially greater distance than said other blade.

5. In a rotary drill bit to be lowered in a well bore: a main body; a cutter supporting member mounted on said body for expansion laterally outward of said body; leading and trailing cutter blades secured to said member; means for expanding said supporting member and cutter blade laterally outward of said body; said cutter blades having bottom cutter edges and side cutter edges; said cutter blades having different negative rakes; the negative rake of said leading blade being substantially greater than the negative rake of said trailing blade; the side cutter edges of said blades being substantially equidistant from the axis of rotation of said main body; said leading blade extending laterally inward from its side cutter edge a substantially greater distance than said trailing blade.

6. In a rotary drill bit to be lowered in a well here: a main body; circumferentially spaced cutter supporting members pivotally mounted on said body for expansion laterally outward of said body; a set of leading and trailing cutter blades adjacent to one another and secured to the lower portion of each of said supporting members; means for expanding said supporting members and sets of cutter blades outwardly of said body; said cutter blades having bottom cutter edges and side cutter edg eneraly parallel to the axis of said body and engageable with the wall of the well bore when said supporting members and sets of blades have been expanded outwardly of sai' body; said leading and trailing cutter blades of each set having negative ralies that are different from each other.

7. In a rotary drill bit to be lowered in a well bore: a main body; circumferentially spaced cutter supporting members pivotally mounted on said body for expansion laterally outward of said body; a set of leading and trailing cutter blades adjacent to one another and secured to the lower portion of each of said supporting members; means for expanding said supporting members and sets of cutter blades outwardly of said body; said cutter blades having bottom cutter edges and side cutter edges generally parallel to the axis of said body and engageable with the wall of the well bore when said supporting members and sets of blades have been expanded outwardly of said body; said leading and trailing cutter blades of each set having negative rakes that are difierent from each other; the negative rake of said leading blade being substantially greater than the negative rake of said trailing blade.

8. In a rotary drill bit to be lowered in a well bore: a main body; circumferentially spaced cutter supporting members pivotally mounted on said body for expansion laterally outward of said body; a set of leading and trailing cutter blades secured to the lower portion of each of said supporting members; means for expanding said supporting members and sets of cutter blades outwardly of said body; said cutter blades having bottom cutter edges and side cutter edges generally parallel to the axis of said body when said supporting members and sets of blades have been expanded outwardly of said body; said leading and trailing cutter blades of each set having negative rakes that are different from each other; the negative rake of said leading blade being substantially greater than the negative rake of said trailing blade; the side cutter edges of the blades of each set being substantially equidistant from the axis of rotation of said main body; said leading blade of each set extending laterally inward from its side cutter edge a substantially greater distance than said trailing blade of the same set.

9. In a rotary drill bit to be lowered in a well bore: a main body; a cutter supporting member mounted on said body for expansion laterally outward of said body; said member having a longitudinal groove extending upwardly thereinto from its lower end; a cutter structure engaging the lower end of said member and having a rib extending upwardly into said groove and a depending cutter blade; means detachably securing said cutter structure to said supporting member; and means for expanding said supporting member and cutter structure laterally outward of said body.

10. In a rotary drill bit to be lowered in a well bore: a main body; a cutter supporting member mounted on said body for expansion laterally outward of said body; said member having a longitudinal groove extending upwardly thereinto from its lower end; a cutter structure including a base engaging the lower end of said member, a rib integral with said base and extending upwardly into said groove, and a cutter blade integral with and depending from said base; means extending through said member and rib detachably securing said structure to said supporting member; and means for expanding said supporting member and cutter structure laterally outward of said body.

11. In a rotary drill bit to be lowered in a well bore: a main body; a cutter supporting member mounted on said body for expansion laterally outward of said body; said member having a longitudinal groove extending up wardly thereinto from its lower end, said groove opening outwardly of said supporting member and being defined by side walls and an upper end wall; said member having a back wall below the lower end of said groove; a cutter structure including a base engaging the lower end of said member and said back wall, a rib integral with said base and extending upwardly into said groove contiguous said side walls and upper end wall, and a cutter blade integral with and depending from said base; means extending through said member and rib detachably securing said structure to said supporting member; and means for expanding said supporting member and cutter structure laterally outward of said body.

12. In a rotary drill bit to be lowered in a well bore: a main body; a cutter supporting member mounted on said body for expansion laterally outward of said body; said member having a longitudinal groove extending upwardly thereinto from its lower end, said groove opening outwardly of said supporting member and being defined by side walls and an upper end wall; said member having a back wall below the lower end of said groove; a cutter structure including a base engaging the lower end of said member and said back wall, a rib integral with said base and extending upwardly into said groove contiguous said side walls and upper end wall, and a cutter blade integral with and depending from said base; said member having aligned holes on opposite sides of said groove; said rib having a hole whose center is off set in a downward and outward direction relative to said aligned holes; and a securing member extending through said supporting member holes and rib hole and engaging the side of said rib hole to urge said cutter structure in an inward and upward direction with respect to said supporting member.

13. In a rotary drill bit to be lowered in a well bore: a main body; a cutter supporting member mounted on said body for expansion laterally outward of said body; 4

said member having a longitudinal groove extending upwardly thereinto from its lower end; a cutter structure engaging the lower end of said member and having a rib extending upwardly into said groove and depending leading and trailing cutter blades having different negative rakes; means detachably securing said cutter struc ture to said supporting member; and means for expanding said supporting member and cutter structure laterally outward of said body.

14. In a rotary drill bit to be lowered in a well bore: a main body; a cutter supporting member mounted on said body for expansion laterally outward of said body; said member having a longitudinal groove extending upwardly thereinto from its lower end; a cutter structure including a base engaging the lower end of said member, a rib integral with said base and extending upwardly into said groove, and leading and trailing cutter blades integral with and depending from said base; said blades having dififerent negative rakes; means extending through said member and rib detachably securing said structure to said supporting member; and means for expanding said supporting member and cutter structure laterally outward of said body.

15. In a rotary drill bit to be lowered in a well bore:

a main body; a cutter supporting member mounted on said 1 body for expansion laterally outward of said body; said member having a longitudinal groove extending upwardly thereinto from its lower end, said groove extending upwardly thereinto from its lower end, said groove opening outwardly of said supporting member and being defined by side walls and an upper end wall; said member having a back wall below the lower end of said groove; a cutter structure including a base engaging the lower end of said member and said back wall, a rib integral with said base and extending upwardly into said groove contiguous said side walls and upper end wall, and trailing and leading cutter blades integral with and depending from said base; said leading and trailing blades both having negative rakes with the rake of said leading blade substantially greater than the rake of said trailing blade; said blades having side cutter edges generally parallel to the axis of said body when said cutter supporting member and cutter structure have been expanded laterally outward of said body; means extending through said member and rib detachably securing said structure to said supporting member; and means for expanding said supporting member and cutter structure laterally outward of said body.

167 In a rotary drill bit to be lowered in a well bore: a main body having a longitudinal slot therein opening outwardly of said body; a cutter supporting member in said slot carried by said body for expansion laterally outward of said body; cutter means on said cutter supporting member; means for expanding said cutter supporting member and cutter means laterally outward of said body; said body having downwardly facing shoulders on opposite sides of said slot diverging in a downward direction; said cutter supporting member having downwardly diverging shoulders on its opposed sides companion to and engageable with said body shoulders upon outward expansion of said cutter supporting member and cutter means.

17. In a drill bit to be lowered in a well bore: a main body; cutter means mounted on said body for expansion laterally outward of said body; means for expanding said cutter means laterally outward of said body; a central passage in said body for drilling fluid having a lower discharge terminus within said body; said body having an enlarged cavity below said terminus into which drilling fluid from said passage can discharge, said body having a wall extending at least partially across the lower portion of said cavity, said body having a lateral opening from the upper portion of said cavity to the exterior of said body adjacent said cutter means when said cutter means is in its outwardly expanded position, whereby fluid discharged from said passage will strike fluid in said cavity and be deflected thereby laterally through said opening toward said cutter means.

18. In a drill bit to be lowered in a well bore: a main body having a longitudinal slot therein; cutter means in said slot carried by said body for expansion laterally outward of said body; means for expanding said cutter means laterally outward of said body; a central passage in said body for drilling fluid having a lower discharge terminus within said body; said body having an enlarged cavity below said terminus and said longitudinal slot into which drilling fluid from said passage can discharge, said body having a wall extending at least partially across the lower portion of said cavity to confine fluid in said cavity, whereby fluid discharge from said passage will strike fluid in said cavity and be deflected laterally through said slot toward said cutter means when said cutter means is in its expanded position.

References Cited in the file of this patent UNITED STATES PATENTS 299,074 Atkinson June 22, 1880 1,406,348 Corrigan Feb. 14, 1922 1,600,783 Youle Sept. 21, 1926 1,913,550 Holt et al June 13, 1933 1,914,735 Clark June 20, 1933 2,485,826 Harinck Oct. 25, 1949 2,545,033 Kammerer Mar. 13, 1951 2,54 5 ,035 Kammerer Mar. 13, 1951 

